524 WILLIAM BATESON. 
In B. minutus the longitudinal muscles of the collar lie in 
a layer immediately under the skin and under the pharyngeal 
wall. The cavity is crossed by many radial fibres, upon which 
some cells are placed, but is not so much filled up as in the 
other species. 
The muscles of the third body cavity are not markedly 
different from those of the collar. In B. Kowalevskii alone 
a large muscular band runs along each side of the ventral 
nerve-cord, forming a projection from the body (v. fig. 108). 
The perihemal cavities are similarly almost filled with 
tissue, and always contain more or less longitudinal muscle- 
fibre. These are gathered into two bundles, and are inserted 
into the notochord sheath in the proboscis stalk. They are 
most developed in B. minutus, &c. (v. figs. 67 and 68). 
The Mesenteries.—The dorsal mesentery persists through- 
out life in B. Kowalevskii and B.salmoneus. In the 
other species it disappears inthe collar region. The 
ventral mesentery persists in the trunk in all species, but 
is always obliterated in the collar. 
In B. minutus the body cavity of the trunk in the hepatic 
region is again divided in consequence of an attachment 
between the lateral angles of the diamond-shaped intestine to 
the body wall (v. fig. 93). In this position two large lateral 
vessels run. 
As Spengel has stated, strands of connective tissue run in 
B. minutus from the body wall between the follicles of the 
ovaries, forming a sort of radial septa. These septa are pro- 
bably not of morphological importance, beyond indicating the 
“ accidental”? way in which such septa may arise (cf. Poly- 
gordius, &c.). 
All the body cavities are full of corpusculated fluid, as Spengel 
has observed. These corpuscles, when living, are full of bright 
granules and vacuoles, and exhibit amceboid movements. 
The Proboscis Gland.—In B. Kowalevskii (fig. 47, 
gis.), at about the age of two gill-slits, a space appears in the 
proliferation of mesoblast lying dorsal to the anterior end of 
the notochord, when the latter is pushed forwards into the 
